Apparatus for examining objects by means of penetrating radiation, typically X-ray or gamma-ray radiation, and for producing cross-section images thereof by the methods of computed tomography is well known and is described, for example, in U.S. Pat. No. 3,778,614 to Hounsfield. In typical CT apparatus the object undergoing X-ray examination is scanned by an X-ray source in combination with one or more X-ray detectors which rotate and/or translate about the object to measure radiation transmission along a large plurality of independent paths in an examination plane. Data obtained from the detectors is then processed and combined, typically by using well known computational algorithms in a digital computer, to generate images of transmissivity characteristics in the plane.
Several computational algorithms are available for generating image information from transmission data. A convolution and backprojection algorithm, of the type first described by Ramachandran and Hakshminarayanan, is generally believed to provide a reasonable compromise between computer equipment cost and image reconstruction time and is utilized, in various forms, in most CT equipment presently in commercial production. Convolution-backprojection algorithms of this type are most efficiently utilized with transmission data measured at discrete points which are uniformly distributed in space. However, the scanning mechanisms which are utilized in the measurement of radiation transmission generally comprise large, high inertia components and tend to translate and/or rotate with time-varying velocity profiles. When data from such mechanisms is sampled at a uniform periodic rate the corresponding transmission paths are not uniformly distributed in space.